In recent years procedures have been developed in which a limb prosthesis (artificial arm or leg) is attached by a bone implant directly to the bone of an amputee's residual limb. As an example of such a procedure, the present applicant's own UK patent application GB-A-2,365,355 describes and illustrates the use of an intra-osseous transcutaneous implant that is secured at a distal end to a limb prosthesis or severed limb and that attaches at a proximal end directly to the bone of the patient's residual limb through the skin. The implant is differentially surface treated, having coatings (e.g. of hydroxy apatite and/or a protein such as laminin or fibronectin to encourage fibrous in-growth) at its proximal end to promote optimal integration with the bone, ligament and skin tissues of the residual limb while having a very low surface energy at its distal (external) end deterring bacterial colonisation at the implant's external skin interface.
The transcutaneous bone implants of GB-A-2,365,355 are relatively securely held in place to the patient's native tissue and are less prone to infection than prior transcutaneous implants. However, in use of these or other direct bone implants for attachment, the attachment can still pose mechanical problems in use. In particular, the joint of the prosthesis to the bone generally has no give and there is a substantial risk that a bending or torsional force applied to the prosthetic limb may either break the bone or cause the bone implant to become detached from it.
The present invention seeks, amongst other objectives, to provide means for addressing the shortcomings of the existing attachments and the bone implant differential coating technology of GB-A-2,365,355 suitably is used in combination with the present invention.